I am struggling to find a way to set up a logical shipping rule that would say "If a customer orders 3 items, THEN use this box for shipping costs" and "IF a customer orders 10 items, THEN use this box for shipping costs." etc.
I only sell 3 items on my store, when a customer orders 1 or 2 items the shipping is ok because my "default box" is big enough to ship either. But when I get an order for 5 or larger, I get hosed on shipping because I need to use a considerably larger box! I would be willing to pay for an app that has this functionality! How does Shopify not have a solution for this yet?
May I know which carrier you are using for handling the shipping process?
As you have mentioned, Shopify only allows you to set up a default box and it doesn't work for merchants having products with different dimensions. The problem with using Shopify's single box size is that you will be undercharging for some orders, and you will be responsible for paying out of pocket for the additional shipping cost. If you overcharge for shipping, customers will abandon their cart.
I would suggest you use the Multi Carrier Shipping Label app, that helps you handle this with ease. With the box packing method in the app, you can set up different packages for your products based on the weight & dimensions. So, whenever your customer places an order, the app automatically chooses the right box and calculates the rates accordingly. Also, with the app, you can print labels, and also automate the tracking process.You can try the app with a 14-day free trial and contact the support for any assistance required.